(1) Field of the Invention
This invention relates to a local signal generation arrangement and, more particularly, to a local signal generation arrangement of the type utilizing the PLL technique and employed in a SSB transmitter and/or receiver employing a method for transmitting and/or receiving an USB and a LSB signals, but not simultaneously.
(2) Description of the Prior Art
Heretofore two methods have principally been used for transmission or reception of the USB and the LSB signals.
One method employs a pair of SSB filters which are used for USB selection and for the LSB, respectively. Another method employs a single SSB filter, and varies the frequency applied to the input of a balanced modulator which produces the amplitude-modulated, carrier suppressed, signal.
The latter method, to which the present invention can be applied, has been frequently used because of lower cost due to the elimination of a very expensive SSB filter, which is usually a crystal filter. However, this method is disadvantageous in that a frequency deviation occurs in the output signal due to changing between USB and LSB modes at the IF stage. To prevent this, the frequency of the local signal generator must be shifted by the amount of the frequency deviation occurring at the IF stage, in order to compensate deviation. A unique method is proposed by the present invention to resolve the above problem.